The thermochemistry and the electrochemical behavior of cytochrome c degradation products, and of judiciously "tailor-made" synthetic analogs, will be studied. Thermodynamics and kinetics of the ferrous-ferric oxidation-reduction process occurring in the prosthetic group will be investigated. Electron transfer reactions implicating univalent, divalent and trivalent cobalt in cobalamines and cobinamides will be explored concomitantly. Experimental methods will include polarography, cyclic voltammetry and adiabatic titration calorimetry.